Radio receiver



Feb.- 25, 1947. D. 0. GRIEG I I 2,416,305

RADIO RECEIVE? I Filed Sept. 18, 1942 2 Sheets-Sheet l i: 1% a i tafilfl E 5 IE il-li H a INVENTOR DONHLO D. GR/EG patented Feb. 25, 1947RADIO RECEIVER Donald D. Grieg, Forest Hills, N. Y., assignor to FederalTelephone and Radio Corporation, a corporation of Delaware ApplicationSeptember 18, 1942, Serial No. 458,854

12 Claims. 1

This invention relates to radio reception and demodulation of timemodulated pulse energy and more particularly to a method and means fortranslating time modulated pulse energy into amplitude modulated pulseenergy. 5 By passing the envelop energy through a low Pulse modulationsystems to which this invenpass filter to remove carrier pulseharmonics, an tion relates generally are disclosed in the U. S. energyoutput in accordance with the modulation Patents to A. Reeves Nos.2,266,401 and 2,256,336; is produced which may be applied directly to aU. S. Patent to E. Deloraine and A. Reeves 2,262,- speaker or otherintelligence translating device. 838; and in copending application of E.Labin en- :51 Should the modulated pulse energy include titled Pulsemodulation system, Serial No. 386,- amplitude modulation as well as timemodulation, 282, filed April 1, 1941; and copending applithe amplitudemodulation may be detected in cation of E. Deloraine and E. LabinentitledPulse known manner and the pulse energy passed to a transmissionsystem, Serial No. 425,103, filed sawtooth generator and clipping devicefor trans- December 31, 1941. .5 lation of the time modulated signals toamplitude In accordance with pulse modulation recurring modulated pulsesfor intelligent reception in acpulses or pairs of pulses, as the casemay be, cordance with the method described above. can be used wherevariations of the spacing be- For a further understanding of the methodtween pulses correspond to signal increments. of this inventionreference may be had to the Where recurring pairs of pulses are used,time accompanying detailed description of a form of modulation maycomprise displacement of the apparatus by which this method may bepracpulses toward and away from each other in pushticed, the detaileddescription to be read in conpull manner or one of each pair may befixed nection with the accompanying drawings, in and the other displacedrelative thereto in acwhich: cordance with a signal increment. While theFig. 1 is a graphical illustration in accordance pairs of pulses may beamplitude modulated as with this invention; well as time modulated forsimultaneous trans- Fig. 2 is a block diagram of a form of apparatusmission of two different signals, this invention is which may be used.in practicing the method; and concerned only with demodulation of thetime Fig. 3 is a schematic illustration of an electrical modulation partthereof. circuit showing details of parts of the apparatus One of theobjects of this invention therefore, of Fig. 2. is to provide a methodand means for demodu- Assuming that a train of pulses is time modulatingtime modulated pulse energy received from lated in accordance with asine wave a (Fig. 1) pulse modulating systems such as those in the thetime modulated relation of the pulses for a aforesaid U. S. Patents andcopending applicycle of the modulating wave is shown by the cations.pulse positions b. The spacing of the pulses is Another object of theinvention is to provide greatly exaggerated for purposes ofillustration, a simplified method and means for translating it beingunderstood that the spacing 151 for untime modulated pulse energy intoamplitude modmodulated pulses having a transmission frequency ulatedpulse energy. 49 of -6 kilocycles, for example, is about 80 micro- Stillanother object of the invention is to proseconds, while the maximumdegree of pulse modvide a method and means for translating time ulationor displacement as indicated by the intermodulated pulse energy intoenvelopes of amval i2 is equal to from one to 2 microseconds plitudemodulation which may be filtered and thereabouts. It will thus be clearthat where applied directly to a speaker. the pulses are observed on theusual oscillograph, Briefly, the method of this invention comprises thedegree of modulation as compared with the generating a wave havingrecurring peaks such, spacing between adjacent pulses is so slight asfor example, as a sawtooth wave, controlling the not to be readilyperceptible. It is this feature amplitudes of the peaks thereof inaccordance of pulse time modulation that is so useful for with thelength of the time intervals between the 50 the sending of secretmessages. pulses of time modulated pulse energy and clip- In the blockdiagram shown in Fig. 2, time ping off the portion of the wave below alevel modulated pulses are first appliedtoa wave gen or threshold suchas is determined by the peak erator 4 adapted to produce a wave havingreamplitude of a wave formed by a time interval curring inclinedportions similar to a sawtooth between pulses corresponding to themaximum shape. For purposes of illustration a pure sawnegativemodulation value. Such a level will provide for demodulation. Thisprovides carrier pulses forming an amplitude envelope in accordance withthe time modulated pulse energy.

tooth wave is used as indicated by the wave (Fig. 1). Alternate teeth ofthe wave thus generated are varied in direct amplitude in proportion tothe time variation of the intervals between adjacent pulses. Thissawtooth wave is then passed through a clipper detector 5 which isbiased to clip off the sawtooth wave below a level 38a such as isdetermined by the amplitude of the sawtooth waves formed in accordancewith the spacing between pulses corresponding to. the maximum negativemodulation value. This clipped portion of the sawtooth wave provides aseries of pulses which form envelope energy such as illustrated by thecurve d. This envelop en-i ergy is then passed through a low pass filter6, for example, of 6 kilocycles for th elimination of carrier pulseharmonics. The output modulated wave from the filter may then be passedto an audio amplifier stage or directly to earphones or a speaker.

Referring more particularly to Figs. 1 and 3, the sawtooth generator isshown to comprise a form of relaxation oscillator having a high vacuumtriode tube 28. The tube is biased through a resistance 22 to a desiredcut-off level. The time modulated pulses are applied to the gridterminal 23. The plate circuit 24 of the tube 26 is supplied with apositive potential through a resistance 25 which functions when theplate current of the tube 20 is cut ofi to charge a condenser 26.Connected to the condenser is a peak rectifier tube eilwhich servesasthe clipper detector. The tube 38 prevents passage therethrough ofsawtooth wave energy below a value or thresh old depending upon thevalue of the negative bias connected through a variable resistor 34 tothe plate circuit 32 thereof. When the tube 20 reaches cut-off andbecomes non-conductive, the potential drop through the resistor 25becomes low and a charge builds up in the condenser 26. The chargingrate of the condenser 26 gives a normal sloping characteristic of thesawtooth oscillation. When this charging potential exceeds the cut-offlevel of the. tube 30, current will begin to flow through the tube 30and resistor 33 and produce a voltage at the out put 35. The cut-offlevel of tube 30, however, is chosen to occur in accordancewith thespacing between pulses corresponding to the maximum negative modulationvalue received at the input terminal 23. .Thus should a pair of suchpulses l0 and l I be received at the terminal 23, the timing of thesawtooth oscillation is such that the impulse ill will operate the tube20 causing the condenser 26 to discharge through the tube 20. Thiscondition is illustrated inFig. 1 by the built-' up slope Illa and thevertical discharge line lDb. Immediately after reception of pulse l0 andthe resulting discharge of condenser 26 the voltage from B+ begins torecharge the condenser. This charging rate is represented by the slopeIla which is parallel to the slope Illa and terminates the instant pulseH is received as indicated by the discharge line I lb. This amplitude ofsawtooth lla is taken as the value at Which the rectifier is biased forpassage of energy, and is represented by the line 30a. At the zero endof the line llb, the condenser 26 begins to recharge forming a slopeI211. The slope lZa continues until the next succeeding pulse I2 isreceived whereupon the amplitude of the sawtooth slope I211 isterminated by the discharge line IZb. Since the pulse I2 is slightlytime modulated, that is, .d isplaced slightly from the position I20,,the slope 12a has had time to build up beyond the cut-01f level 35a.Thus, a small amount of energy represented by the peak l2d extendingbeyond the line etc has passed through the tube 30. The next succeedingpulse it, however, is time modulated in an opposite direction from thedirection of modulation of the pulse l2 so that the next sawtooth slope53% does not reach the amplitude level of the line 3311 by the time thepulse I3 is received. Thus the sawtooth slope [3a is terminated belowthe line 36a.

It will be seen that time modulation in accordance with the sine wave a,provides alternately high and low pulses in accordance with the degreeof modulation. The peaks of the high amplitude sawteeth comprise carrierpulses and together form an envelope d in accordance with the timemodulation of the pulses.

While I have shown for purposes of illustration a'modulation inaccordance with a sine wave, it will be clear that modulation by voiceor other forms of signals maybe transmitted by time modulation anddemodulated in accordance with this invention to provide 'a translationto amplitude pulse modulation. This amplitude modulation is provided bythe sawtooth peaks which provide a substantial amount of energy for thewave. The envelope wave, however, may be passed through anaudio-amplifier or after having been filtered to remove the carrierpulses may be passed directly to a speaker. I

It will be recognized that demodulation in accordance to this inventionis applicable to various forms of pulse modulation wherever themodulation is efiected by variation of the spacing or time intervalsbetween pulses. Thus, even for pairs of pulses where one pulse recurs atfixed intervals and the other pulse occurs at varying intervals inaccordance with modulation, the variation of spacing between adjacentpulses of a wave train of each pulse pairs can be used to control thebuild-up of wave peaks as hereinbefore described. Likewise, where thepulse pairs are spaced apart a larger interval than the spacing of thepulses of each pair, the time modulation of the pulses of each pairprovide variation in spacing between the pulses of a wave train thereofwhereby translation to amplitude modulation may bemade in accordancewith this invention.

While I have shown and described but one form of apparatus by which themethod of this invention may be practiced, I recognize that otherapparatus as well as variations of the form of apparatus herein shownand described may be made without departing from the invention. It willbe understood, therefore, that the form of apparatus herein shown anddescribed is to be regarded as illustrative of the invention only andnot as restricting the appended claims.

What is claimed is:

1. A method for translating a train of time modulated pulse energy intoan amplitude modulated pulse Wave, comprising initiating generation of aperiod of said wave having voltage increasing according to a givenpattern with time in accordance with the occurrence of a pulse of saidtime modulated pulse energy, terminatingsaid generation and initiatinggeneration of a new period of said wave by the occurrence of'thegeneration of a period of said wave. in accord,-

ance. with the occurrence of a pulse of said time modulated pulseenergy, said period being in the form of a sawtooth, terminating saidgeneration and initiating generation of a new sawtooth period by theoccurrence of the next succeeding pulse of said time modulated pulseenergy, and threshold clipping said wave at an amplitude correspondingto the amplitude of a sawtooth produced by two succeeding pulses ofmaximum neg ative modulation.

3. A method for translating a train of time mod? ulated pulse energyinto an amplitude modulated pulse wave comprising initiating generationof a period of said wave having voltage increasing according to a givenpattern with time in accordance with the occurrence of a pulse of saidtime modulated pulse energy, terminating said genera tion and initiatinggeneration of a new period of .3

said wave by the occurrence of the next succeeding pulse of said timemodulated pulse ener y, threshold clipping said wave at an amplitudecol"- responding to the amplitude of a period of said wave produced bytwo succeeding pulses of maximum negative modulation, thereby providingan amplitude envelope in accordance with time modulation of said pulseenergy, and filteringthe envelope energy to remove pulse harmonics.

4. A method for translating a train of time modulated pulse energy intoan amplitude modulated wave, wherein succeeding pairs of pulses definesignal increments by the relative time displacement of said pulses inaccordance with a modulating signal Wave, said time modulated pulsesbeing characterized by the alternate and intermediate pulses beingdisplaced in push-pull manner toward or away from their succeedingpulses according to the instantaneous amplitude of the signal wave withwhich said pulses are modulated; said method comprising initiatinggeneration of a sawtooth voltage by the occurrence of one of the pulsesof said timemodulated pulses, terminating the sawtooth generation andinitiating generation of a new sawtooth by the occurrence of the nextsucceeding pulse of said time modulated pulses, and threshold clippingsaid sawtooth voltage at an amplitude level determined by the amplitudeof a sawtooth produced by two succeeding pulses of maximum negativemodulation, thereby obtaining a succession of sawtooth pulses definingenvelopes corresponding to the modulating signal wave.

5. A method for translating a train of time modulated pulses into anamplitude modulated signal wave, said time modulated pulses beingcharacterized by the alternate and intermediate pulses being displacedtoward or away from their succeeding pulse according to theinstantaneous amplitude of the signal wave with which said pulses aremodulated; comprising initiating generation of a sawtooth voltage by theoccurrence of one of the pulses of said time modulated pulses,terminating the sawtooth generation and initiating generation of a newsawtooth by the occurrence of the neXt succeeding pulse of said timemodulated pulses, threshold clipping said sawtooth voltage at anamplitude level determined by the amplitude of a sawtooth produced bytwo succeeding pulses of maximum negative modulation, thereby definingamplitude envelopes in accordance with time modulation of said pulse en-6 v S. ergy, and. filtering; the envelope energy to re, move pulseharmonics.

6. A demodulator for translating a. trainof time modulated pulse energyinto amplitude modulated. pulse energy wherein the said time modulatedpulses are characterized by at least one set of alternate pulses beingdisplaced toward or away from the intermediate pulses according to theinstantaneous amplitude of the signal wave with which said pulses aremodulated; comprising generator means to generate a voltage waveincreasing according to a given pattern with time, means controllingoperation of said generator means in accordance with the pulses of saidtime modulated pulse energy, whereby generation of a period of saidvoltage wave is terminated and a. new period is initiated by each pulse,the amplitude of theperiods being thereby controlled in accordance withthe time intervals occurring between succeeding pulses of the timemodulated pulse energy, and means to clip off the portion of saidvoltage wave below a level determined by the amplitude of two succeedingpulses whose modulation is of maximum negative value thereby providingamplitude envelope energy in accordance with the time modulation of saidtrain of pulse energy.

7. The demodulator defined in claim 6 wherein .the voltage wavegenerating means comprises a relaxation oscillator.

8. The demodulator defined in claim 6 wherein the Wave clipping meanscomprises a peak'rectifier.

9. The demodulator defined in claim 6 wherein the voltage wavegenerating means comprises a relaxation oscillator and the clippingmeans comprises a peak rectifier.

10. A demodulator for translating time modulated pulse energy intoamplitude modulated energy wherein pairs of pulses define signalincrements by relative time displacement of the pulses in accordancewith a modulating signal wave, said time modulated pulses beingcharacterized by the alternate and intermediate pulses being displacedin push-pull manner toward or away from their succeeding pulsesaccording to the instantaneous amplitude of the signal wave, comprisingmeansto generate an energy wave of generally sawtooth form, means tocontrol the amplitude of the sawteeth in accordance with the timeintervals occurring between pulses of the time modulated pulse energy,the varying of the time interval between pulses resulting in alternatelyhigh and low sawteeth, means to clip ofi the portion of said wave belowan amplitude determined by a sawtooth formed in accordance with thespacing between unmodulated pulses, thereby providing envelope energy ofsawteeth energy exceeding the clipping amplitude, and means to filterthe envelope energy to remove pulse harmonics therefrom.

11. A modulator for translating time modulated pulse energy intoamplitude modulated pulse energy, comprising a relaxation oscillator togenerate a sawtooth wave, means to control the operation of therelaxation oscillator in accordance with the lapse of time betweenadjacent pulses of the time modulated pulse energy so that theamplitudes of the sawteeth of said wave correspond with the timeintervals between adjacent pulses, and a peak rectifier connected to theoutput of said oscillator arranged to only pass sawtooth energy above anamplitude level determined by the amplitude of two pulses of maximumnegative modulation whereby amplitude'envelope energy is produced inaccordance with the v j modulation of said time modulated pulse energy.-.12. A method for translating a train of time. i modulated, pulses intoaniamplitude modulated wave, wherein the said time modulated pulses 5are characterized by at least one set of alternate pulsesbeing displacedtoward or away from the I intermediate pulses according to.the'instanta- 1 neous amplitude of the signal wave with which saidpulses are modulated, comprising initiating 5 generation of a sawtoothvoltage by the occur- 1 rence of one of the pulses of said timemodulated pulses; terminating the sawtooth generation and initiatinggeneration of a new sawtooth by the I occurrence of the next succeedingpulse of said 3 time modulated pulses, and threshold clipping saidsawtooth voltage-at an amplitude level determined by the, amplitude of asawtooth voltage produced by two succeeding. pulses of maxi mum negativemodulation.

DONALD D. GRIEG.

REFERENCES CITED 2 The following references are of record in the file ofthis patent:

UNITED STATES PATENTS 10' Number Name Date 1,655,543 Heising Jan, 10,1928 2,227,596 Luck Jan. 7, 1941 2,266,401 Reeves Dec. 16, 19412,061,734 Kell Nov. 24, 1936 2,218,642 Hathaway Oct. 22, 1940 FOREIGNPATENTS Number Country Date 348,656 Italy Feb. 8, 1937

